Wireless communication method for saving power and wireless communication terminal using same

ABSTRACT

The present invention relates to a wireless communication method for power saving and a wireless communication terminal using the same, and more particularly, to a wireless communication method for efficiently conducting data transmission/reception of each terminal in a high density environment and a wireless communication terminal using the same. To this end, the present invention provides a wireless communication method for a terminal including receiving a distributed access group parameter for data transmission/reception by a group unit, wherein the distributed access group parameter comprises information about a number of groups assigned to a corresponding BSS, obtaining group information about the terminal based on the distributed access group parameter, and performing data transmission based on the obtained group information, and a wireless communication terminal using the same.

TECHNICAL FIELD

The present invention relates to a wireless communication method forpower saving and a wireless communication terminal using the same, andmore particularly, to a wireless communication method for efficientlyconducting data transmission/reception of each terminal in a highdensity environment and a wireless communication terminal using thesame.

BACKGROUND ART

In recent years, with supply expansion of mobile apparatuses, a wirelessLAN technology that can provide a rapid wireless Internet service to themobile apparatuses has been significantly spotlighted. The wireless LANtechnology allows mobile apparatuses including a smart phone, a smartpad, a laptop computer, a portable multimedia player, an embeddedapparatus, and the like to wirelessly access the Internet in home or acompany or a specific service providing area based on a wirelesscommunication technology in a short range.

Institute of Electrical and Electronics Engineers (IEEE) 802.11 hascommercialized or developed various technological standards since aninitial wireless LAN technology is supported using frequencies of 2.4GHz. First, the IEEE 802.11b supports a communication speed of a maximumof 11 Mbps while using frequencies of a 2.4 GHz band. IEEE 802.11a whichis commercialized after the IEEE 802.11b uses frequencies of not the 2.4GHz band but a 5 GHz band to reduce an influence by interference ascompared with the frequencies of the 2.4 GHz band which aresignificantly congested and improves the communication speed up to amaximum of 54 Mbps by using an OFDM technology. However, the IEEE802.11a has a disadvantage in that a communication distance is shorterthan the IEEE 802.11b. In addition, IEEE 802.11g uses the frequencies ofthe 2.4 GHz band similarly to the IEEE 802.11b to implement thecommunication speed of a maximum of 54 Mbps and satisfies backwardcompatibility to significantly come into the spotlight and further, issuperior to the IEEE 802.11a in terms of the communication distance.

Moreover, as a technology standard established to overcome a limitationof the communication speed which is pointed out as a weak point in awireless LAN, IEEE 802.11n has been provided. The IEEE 802.11n aims atincreasing the speed and reliability of a network and extending anoperating distance of a wireless network. In more detail, the IEEE802.11n supports a high throughput (HT) in which a data processing speedis a maximum of 540 Mbps or more and further, is based on a multipleinputs and multiple outputs (MIMO) technology in which multiple antennasare used at both sides of a transmitting unit and a receiving unit inorder to minimize a transmission error and optimize a data speed.Further, the standard can use a coding scheme that transmits multiplecopies which overlap with each other in order to increase datareliability.

As the supply of the wireless LAN is activated and further, applicationsusing the wireless LAN are diversified, the need for new wireless LANsystems for supporting a higher throughput (very high throughput (VHT))than the data processing speed supported by the IEEE 802.11n has comeinto the spotlight. Among them, IEEE 802.11ac supports a wide bandwidth(80 to 160 MHz) in the 5 GHz frequencies. The IEEE 802.11ac standard isdefined only in the 5 GHz band, but initial 11ac chipsets will supporteven operations in the 2.4 GHz band for the backward compatibility withthe existing 2.4 GHz band products. Theoretically, according to thestandard, wireless LAN speeds of multiple stations are enabled up to aminimum of 1 Gbps and a maximum single link speed is enabled up to aminimum of 500 Mbps. This is achieved by extending concepts of a radiointerface accepted by 802.11n, such as a wider radio frequency bandwidth(a maximum of 160 MHz), more MIMO spatial streams (a maximum of 8),multi-user MIMO, and high-density modulation (a maximum of 256 QAM).Further, as a scheme that transmits data by using a 60 GHz band insteadof the existing 2.4 GHz/5 GHz, IEEE 802.11ad has been provided. The IEEE802.11ad is a transmission standard that provides a speed of a maximumof 7 Gbps by using a beamforming technology and is suitable for high bitrate moving picture streaming such as massive data or non-compression HDvideo. However, since it is difficult for the 60 GHz frequency band topass through an obstacle, it is disadvantageous in that the 60 GHzfrequency band can be used only among devices in a short-distance space.

Meanwhile, in recent years, as next-generation wireless LAN standardsafter the 802.11ac and 802.11ad, discussion for providing ahigh-efficiency and high-performance wireless LAN communicationtechnology in a high-density environment is continuously performed. Thatis, in a next-generation wireless LAN environment, communication havinghigh frequency efficiency needs to be provided indoors/outdoors underthe presence of high-density stations and access points (APs) andvarious technologies for implementing the communication are required.

DISCLOSURE Technical Problem

The present invention provides wireless LAN communication with highefficiency/high performance in a high density environment.

The present invention also provides a method for efficiently conductingdata transmission/reception of terminals in a power saving mode.

The present invention also provides a method for reducing thepossibility of collision during data transmission by a plurality ofterminals in a dense user environment and providing a stable datacommunication environment.

In addition, the present invention also enables a plurality of terminalsto perform distributed data transmission using multi-channels.

Technical Solution

In order to solve the above-described technical problems, the presentinvention provides the following wireless communication method andwireless communication terminal.

The present invention provides a wireless communication method for aterminal including: receiving a distributed access group parameter fordata transmission/reception by a group unit, wherein the distributedaccess group parameter comprises information of the number of groupsassigned to a corresponding BSS; obtaining group information of theterminal based on the distributed access group parameter; and performingdata transmission based on the obtained group information.

In addition, the present invention provides a wireless communicationterminal including: a transceiver for transmitting and receiving awireless signal; and a processor for controlling an operation of theterminal, wherein the processor receives a distributed access groupparameter for data transmission/reception by a group unit, wherein thedistributed access group parameter comprises information of the numberof groups assigned to a corresponding BSS, obtains group information ofthe terminal based on the distributed access group parameter, andperforms data transmission based on the obtained group information.

In an embodiment of the present invention, the performing datatransmission may be characterized in that at least one terminal havingidentical group information participates in the data transmission duringa predetermined access period.

In an embodiment of the present invention, the at least one terminalhaving the identical group information may simultaneously transmit databy using different channels with each other.

In an embodiment of the present invention, the at least one terminalhaving the identical group information may sequentially transmit data.

In an embodiment of the present invention, the at least one terminalhaving identical group information may perform a backoff procedure forthe data transmission during the predetermined access period.

In an embodiment of the present invention, the distributed access groupparameter may further comprise inter-group access offset information,wherein the predetermined access period is terminated when a channel isidle for the inter-group access offset time.

In an embodiment of the present invention, the predetermined accessperiod may be set to be a fixed time value.

In an embodiment of the present invention, when the predetermined accessperiod is terminated, terminals having group information of a nextaccess order may participate in the data transmission.

In an embodiment of the present invention, the group information of theterminal may be determined based on information of the number of groupsand identifier information of the terminal.

In an embodiment of the present invention, the group information of theterminal may be determined based on a value obtained by modulo-operatingthe identifier information of the terminal with the number of groups.

In an embodiment of the present invention, the information of the numberof groups may be changed based on a duration of an access period of anindividual group.

In an embodiment of the present invention, the distributed access groupparameter may be transmitted through a beacon or a probe response.

In an embodiment of the present invention, the distributed access groupparameter may further comprise access start offset informationrepresenting a time point at which terminals of each group start access.

Next, the present invention provides a wireless communication method fora target terminal including: receiving a trigger frame for indicatingdownlink data to be transmitted to each terminal of a BSS throughmulti-channels; obtaining target channel information for receiving thedownlink data, when the trigger frame indicates that there is downlinkdata to be transmitted to the target terminal; and receiving thedownlink data through the target channel.

In addition, the present invention provides the target terminal forwireless communication including: a transceiver for transmitting andreceiving a wireless signal; and a processor for controlling anoperation of the target terminal, wherein the processor receives atrigger frame for indicating downlink data to be transmitted to eachterminal of a BSS through multi-channels, obtains information of atarget channel for receiving the downlink data, when the trigger frameindicates that there is downlink data to be transmitted to the targetterminal, and receives the downlink data through the target channel.

At this point, each of the terminals in the BSS, which include thetarget terminal, may simultaneously receive downlink data using themulti-channels.

In addition, the wireless communication method may further includetransmitting, through the target channel, a data request frame whichrepresents presence of the target terminal in response to the triggerframe.

At this point, the wireless communication method may further includeperforming a backoff procedure in the target channel to transmit thedata request frame.

Here, when a backoff counter in the backoff procedure has expired andthe target terminal has transmitted the data request frame, downlinkdata may be received to the target terminal through the target channel.

According to an embodiment, the target channel may be determined basedon an identifier of the target terminal and information of the number ofavailable channels in the BSS.

In detail, the target channel may be determined based on a valueobtained by modulo-operating the identifier of the target terminal withthe information of the number of the available channels.

At this point, the identifier of the target terminal may be any one of aMAC address or an association ID of the target terminal.

According to another embodiment, the target channel may be determinedbased on an order in which the target terminal is indicated in thetrigger frame and information of the number of the available channels inthe BSS.

In detail, the target channel may be determined based on a valueobtained by modulo-operating the order in which the target terminal isindicated among terminals, which are indicated by the trigger frame thatthere is downlink data to be transmitted, with the information of thenumber of the available channels in the BSS.

According to an embodiment, the trigger frame may be a trafficindication map (TIM).

In addition, the trigger frame may include the information of the numberof the available channels in the BSS.

In addition, the data request frame may be a PS-Poll.

According to an embodiment of the present invention, each of theterminals in the BSS may be a terminal in a power saving mode.

According to another embodiment of the present invention, thetransmission of the data request frame and reception of the downlinkdata may be respectively performed in separately allocated periods.

In addition, a period of the transmission of the data request frame anda period of the reception of the downlink data may be repeated aplurality of times.

At this point, information of the number of repetitions may be includedin the trigger frame.

According to an embodiment, the data request frame may include durationinformation until the end of the data request frame transmission periodand each terminal in the BSS having received the data request frame mayset a Network Allocation Vector (NAV) based on the duration information.

At this point, the data request frame may include a combined transmitteraddress field, and the combined transmitter address field may beconfigured to include an association ID of a terminal that transmits thedata request frame and partial lower information of a MAC address of theterminal.

According to an embodiment of the present invention, the downlink datamay be aggregated data for a plurality of terminals.

At this point, the aggregated data includes an A-MPDU configured byaggregating a plurality of MPDUs for each terminal.

In addition, the aggregated data is configured by aggregating aplurality of A-MPDUs.

According to an embodiment of the present invention, an RTS-to-selfframe for setting the data request frame transmission period may befurther received.

At this point, both a receiver address and a transmitter address of theRTS-to-self frame may be set to a MAC address of an AP operating theBSS.

In addition, duration field of the RTS-to-self frame may represent atime until the end of the data request frame transmission period.

According to another embodiment of the present invention, the datarequest frame transmission period may be configured with at least oneslot and a transmission opportunity of data request frame of oneterminal is assigned for each slot.

At this point, the trigger frame may include a slot number fieldrepresenting information on how many slots configure the data requestframe transmission period in a time axis.

In addition, a sequence of the data request frame transmission periodallocated to the terminal may be determined based on the number ofslots, the number of available channels in the BSS, and an order inwhich the target terminal is indicated in the trigger frame.

In addition, a target channel and a slot through which the terminal willtransmit the data request frame in the allocated sequence may bedetermined based on the number of slots, the number of availablechannels in the BSS, and an order in which the target terminal isindicated in the trigger frame.

Advantageous Effects

According to an embodiment of the present invention, it is possible toreduce the time required for access by reducing the possibility ofcollision of data transmission between terminals in a dense userenvironment.

In addition, according to an embodiment of the present invention, sincea period in which terminals with data to be received can transmit datarequest frames is guaranteed, each terminal may swiftly receive data.

In addition, according to an embodiment of the present invention, sincedata for a plurality of terminals is aggregated to be transmitted, anoverhead for data transmission may be reduced.

According to an embodiment of the present invention, the entire resourceutilization ratio may be increased and performance of a wireless LANsystem may be improved in a contention-based channel access system.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a wireless LAN system according to an embodiment ofthe present invention.

FIG. 2 illustrates a wireless LAN system according to another embodimentof the present invention.

FIG. 3 is a block diagram illustrating a configuration of a stationaccording to an embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of an accesspoint according to an embodiment of the present invention.

FIG. 5 schematically illustrates a process in which a STA establishes alink with an AP.

FIG. 6 illustrates a Carrier Sense Multiple Access (CSMA)/CollisionAvoidance (CA) method used in a wireless LAN communication.

FIG. 7 illustrates a method for performing a Distributed CoordinationFunction (DCF) using a Request to Send (RTS) frame and a Clear to Send(CTS) frame.

FIGS. 8 to 10 illustrate a wireless communication method for a terminalusing a distributed access group.

FIG. 11 illustrates a data transmission method using a TIM and a PS-Pollin a power saving mode.

FIG. 12 illustrates an embodiment of a data request frame fordistributed data transmission using multi-channels.

FIGS. 13 to 18 illustrate distributed data transmission methods usingmulti-channels according to a first embodiment of the present invention.

FIG. 19 illustrates another embodiment of a data request frame fordistributed data transmission using multi-channels.

FIGS. 20 to 25 illustrate distributed data transmission methods usingmulti-channels according to a second embodiment of the presentinvention.

FIG. 26 illustrates an RTS-to-self frame for setting a PS pollingperiod.

FIGS. 27 and 28 illustrate distributed data transmission methods usingmulti-channels according to a third embodiment of the present invention.

FIG. 29 illustrates another embodiment of a trigger frame for indicatingdownlink data to be transmitted to each terminal through multi-channels.

FIGS. 30 and 31 illustrate distributed data transmission methods usingmulti-channels according to a fourth embodiment of the presentinvention.

BEST MODE

Terms used in the specification adopt general terms which are currentlywidely used by considering functions in the present invention, but theterms may be changed depending on an intention of those skilled in theart, customs, and emergence of new technology. Further, in a specificcase, there is a term arbitrarily selected by an applicant and in thiscase, a meaning thereof will be described in a corresponding descriptionpart of the invention. Accordingly, it should be revealed that a termused in the specification should be analyzed based on not just a name ofthe term but a substantial meaning of the term and contents throughoutthe specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. Further, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.Moreover, limitations such as “or more” or “or less” based on a specificthreshold may be appropriately substituted with “more than” or “lessthan”, respectively.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2014-0076101, 10-2014-0076388, 10-2014-0080250 and10-2014-0083847 filed in the Korean Intellectual Property Office and theembodiments and mentioned items described in the respective applicationsare included in the Detailed Description of the present application.

FIG. 1 is a diagram illustrating a wireless LAN system according to anembodiment of the present invention. The wireless LAN system includesone or more basic service sets (BSS) and the BSS represents a set ofapparatuses which are successfully synchronized with each other tocommunicate with each other. In general, the BSS may be classified intoan infrastructure BSS and an independent BSS (IBSS) and FIG. 1illustrates the infrastructure BSS between them.

As illustrated in FIG. 1, the infrastructure BSS (BSS1 and BSS2)includes one or more stations STA1, STA2, STA3, STA4, and STA5, accesspoints PCP/AP-1 and PCP/AP-2 which are stations providing a distributionservice, and a distribution system (DS) connecting the multiple accesspoints PCP/AP-1 and PCP/AP-2.

The station (STA) is a predetermined device including medium accesscontrol (MAC) following a regulation of an IEEE 802.11 standard and aphysical layer interface for a radio medium, and includes both anon-access point (non-AP) station and an access point (AP) in a broadsense. Further, in the present specification, a term ‘terminal’ may beused to refer to a non-AP STA, or an AP, or to both terms. A station forwireless communication includes a processor and a transceiver andaccording to the embodiment, may further include a user interface unitand a display unit. The processor may generate a frame to be transmittedthrough a wireless network or process a frame received through thewireless network and besides, perform various processing for controllingthe station. In addition, the transceiver is functionally connected withthe processor and transmits and receives frames through the wirelessnetwork for the station.

The access point (AP) is an entity that provides access to thedistribution system (DS) via wireless medium for the station associatedtherewith. In the infrastructure BSS, communication among non-APstations is, in principle, performed via the AP, but when a direct linkis configured, direct communication is enabled even among the non-APstations. Meanwhile, in the present invention, the AP is used as aconcept including a personal BSS coordination point (PCP) and mayinclude concepts including a centralized controller, a base station(BS), a node-B, a base transceiver system (BTS), and a site controllerin a broad sense.

A plurality of infrastructure BSSs may be connected with each otherthrough the distribution system (DS). In this case, a plurality of BSSsconnected through the distribution system is referred to as an extendedservice set (ESS).

FIG. 2 illustrates an independent BSS which is a wireless LAN systemaccording to another embodiment of the present invention. In theembodiment of FIG. 2, duplicative description of parts, which are thesame as or correspond to the embodiment of FIG. 1, will be omitted.

Since a BSS3 illustrated in FIG. 2 is the independent BSS and does notinclude the AP, all stations STA6 and STA7 are not connected with theAP. The independent BSS is not permitted to access the distributionsystem and forms a self-contained network. In the independent BSS, therespective stations STA6 and STA7 may be directly connected with eachother.

FIG. 3 is a block diagram illustrating a configuration of a station 100according to an embodiment of the present invention.

As illustrated in FIG. 3, the station 100 according to the embodiment ofthe present invention may include a processor 110, a transceiver 120, auser interface unit 140, a display unit 150, and a memory 160.

First, the transceiver 120 transmits and receives a radio signal such asa wireless LAN packet, or the like and may be embedded in the station100 or provided as an exterior. According to the embodiment, thetransceiver 120 may include at least one transmit/receive module usingdifferent frequency bands. For example, the transceiver 120 may includetransmit/receive modules having different frequency bands such as 2.4GHz, 5 GHz, and 60 GHz. According to an embodiment, the station 100 mayinclude a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the AP or an external station according to a wirelessLAN standard of a frequency band supported by the correspondingtransmit/receive module. The transceiver 120 may operate only onetransmit/receive module at a time or simultaneously operate multipletransmit/receive modules together according to the performance andrequirements of the station 100. When the station 100 includes aplurality of transmit/receive modules, each transmit/receive module maybe implemented by independent elements or a plurality of modules may beintegrated into one chip.

Next, the user interface unit 140 includes various types of input/outputmeans provided in the station 100. That is, the user interface unit 140may receive a user input by using various input means and the processor110 may control the station 100 based on the received user input.Further, the user interface unit 140 may perform output based on acommand of the processor 110 by using various output means.

Next, the display unit 150 outputs an image on a display screen. Thedisplay unit 150 may output various display objects such as contentsexecuted by the processor 110 or a user interface based on a controlcommand of the processor 110, and the like. Further, the memory 160stores a control program used in the station 100 and various resultingdata. The control program may include an access program required for thestation 100 to access the AP or the external station.

The processor 110 of the present invention may execute various commandsor programs and process data in the station 100. Further, the processor110 may control the respective units of the station 100 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 110 may execute the program foraccessing the AP stored in the memory 160 and receive a communicationconfiguration message transmitted by the AP. Further, the processor 110may read information on a priority condition of the station 100 includedin the communication configuration message and request the access to theAP based on the information on the priority condition of the station100. The processor 110 of the present invention may represent a maincontrol unit of the station 100 and according to the embodiment, theprocessor 110 may represent a control unit for individually controllingsome component of the station 100, for example, the transceiver 120, andthe like. The processor 110 controls various operations of radio signaltransmission/reception of the station 100 according to the embodiment ofthe present invention. A detailed embodiment thereof will be describedbelow.

The station 100 illustrated in FIG. 3 is a block diagram according to anembodiment of the present invention, where separate blocks areillustrated as logically distinguished elements of the device.Accordingly, the elements of the device may be mounted in a single chipor multiple chips depending on design of the device. For example, theprocessor 110 and the transceiver 120 may be implemented while beingintegrated into a single chip or implemented as a separate chip.Further, in the embodiment of the present invention, some components ofthe station 100, for example, the user interface unit 140 and thedisplay unit 150 may be optionally provided in the station 100.

FIG. 4 is a block diagram illustrating a configuration of an AP 200according to an embodiment of the present invention.

As illustrated in FIG. 4, the AP 200 according to the embodiment of thepresent invention may include a processor 210, a transceiver 220, and amemory 260. In FIG. 4, among the components of the AP 200, duplicativedescription of parts which are the same as or correspond to thecomponents of the station 100 of FIG. 2 will be omitted.

Referring to FIG. 4, the AP 200 according to the present inventionincludes the transceiver 220 for operating the BSS in at least onefrequency band. As described in the embodiment of FIG. 3, thetransceiver 220 of the AP 200 may also include a plurality oftransmit/receive modules using different frequency bands. That is, theAP 200 according to the embodiment of the present invention may includetwo or more transmit/receive modules among different frequency bands,for example, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP 200may include a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the station according to a wireless LAN standard of afrequency band supported by the corresponding transmit/receive module.The transceiver 220 may operate only one transmit/receive module at atime or simultaneously operate multiple transmit/receive modulestogether according to the performance and requirements of the AP 200.

Next, the memory 260 stores a control program used in the AP 200 andvarious resulting data. The control program may include an accessprogram for managing the access of the station. Further, the processor210 may control the respective units of the AP 200 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 210 may execute the program foraccessing the station stored in the memory 260 and transmitcommunication configuration messages for one or more stations. In thiscase, the communication configuration messages may include informationabout access priority conditions of the respective stations. Further,the processor 210 performs an access configuration according to anaccess request of the station. The processor 210 controls variousoperations such as radio signal transmission/reception of the AP 200according to the embodiment of the present invention. A detailedembodiment thereof will be described below.

FIG. 5 is a diagram schematically illustrating a process in which a STAsets a link with an AP.

Referring to FIG. 5, the link between the STA 100 and the AP 200 is setthrough three steps of scanning, authentication, and association in abroad way. First, the scanning step is a step in which the STA 100obtains access information of BSS operated by the AP 200. A method forperforming the scanning includes a passive scanning method in which theAP 200 obtains information by using a beacon message (S101) which isperiodically transmitted and an active scanning method in which the STA100 transmits a probe request to the AP (S103) and obtains accessinformation by receiving a probe response from the AP (S105).

The STA 100 that successfully receives wireless access information inthe scanning step performs the authentication step by transmitting anauthentication request (S107 a) and receiving an authentication responsefrom the AP 200 (S107 b). After the authentication step is performed,the STA 100 performs the association step by transmitting an associationrequest (S109 a) and receiving an association response from the AP 200(S109 b).

Meanwhile, an 802.1X based authentication step (S111) and an IP addressobtaining step (S113) through DHCP may be additionally performed. InFIG. 5, the authentication server 300 is a server that processes 802.1Xbased authentication with the STA 100 and may be present in physicalassociation with the AP 200 or present as a separate server.

FIG. 6 is a diagram illustrating a carrier sense multiple access(CSMA)/collision avoidance (CA) method used in wireless LANcommunication.

A terminal that performs a wireless LAN communication checks whether achannel is busy by performing carrier sensing before transmitting data.When a radio signal having a predetermined strength or more is sensed,it is determined that the corresponding channel is busy and the terminaldelays the access to the corresponding channel. Such a process isreferred to as clear channel assessment (CCA) and a level to decidewhether the corresponding signal is sensed is referred to as a CCAthreshold. When a radio signal having the CCA threshold or more, whichis received by the terminal, indicates the corresponding terminal as areceiver, the terminal processes the received radio signal. Meanwhile,when a radio signal is not sensed in the corresponding channel or aradio signal having a strength smaller than the CCA threshold is sensed,it is determined that the channel is idle.

When it is determined that the channel is idle, each terminal havingdata to be transmitted performs a backoff procedure after an interframespace (IFS) time depending on a situation of each terminal, forinstance, an arbitration IFS (AIFS), a PCF IFS (PIFS), or the likeelapses. According to the embodiment, the AIFS may be used as acomponent which substitutes for the existing DCF IFS (DIFS). Eachterminal stands by while decreasing slot time(s) as long as a randomnumber allocated to the corresponding terminal during an interval of anidle state of the channel and a terminal that completely exhausts theslot time(s) attempts to access the corresponding channel. As such, aninterval in which each terminal performs the backoff procedure isreferred to as a contention window interval.

When a specific terminal successfully accesses the channel, thecorresponding terminal may transmit data through the channel. However,when the terminal which attempts the access collides with anotherterminal, the terminals which collide with each other are allocated withnew random numbers, respectively to perform the backoff procedure again.According to an embodiment, a random number newly allocated to eachterminal may be decided within a range (2*CW) which is twice larger thana range (a contention window, CW) of a random number which thecorresponding terminal is previously allocated with. Meanwhile, eachterminal attempts the access by performing the backoff procedure againin a next contention window interval and in this case, each terminalperforms the backoff procedure from slot time(s) which remained in theprevious contention window interval. By such a method, the respectiveterminals that perform the wireless LAN communication may avoid a mutualcollision for a specific channel.

FIG. 7 is a diagram illustrating a method for performing a distributedcoordination function using a request to send (RTS) frame and a clear tosend (CTS) frame.

The AP and STAs in the BSS contend in order to obtain an authority fortransmitting data. When data transmission at the previous step iscompleted, each terminal having data to be transmitted performs abackoff procedure while decreasing a backoff counter (alternatively, abackoff timer) of a random number allocated to each terminal after anAFIS time. A transmitting terminal in which the backoff counter hasexpired transmits the request to send (RTS) frame to notify thatcorresponding terminal has data to transmit. According to an exemplaryembodiment of FIG. 7, STA1 which holds a lead in contention with minimumbackoff may transmit the RTS frame after the backoff counter hasexpired. The RTS frame includes information on a receiver address, atransmitter address, and duration. A receiving terminal (i.e., the AP inFIG. 7) that receives the RTS frame transmits the clear to send (CTS)frame after waiting for a short IFS (SIFS) time to notify that the datatransmission is available to the transmitting terminal STA1. The CTSframe includes the information on a receiver address and duration. Inthis case, the receiver address of the CTS frame may be set identicallyto a transmitter address of the RTS frame corresponding thereto, thatis, an address of the transmitting terminal STA1.

The transmitting terminal STA1 that receives the CTS frame transmits thedata after a SIFS time. When the data transmission is completed, thereceiving terminal AP transmits an acknowledgment (ACK) frame after aSIFS time to notify that the data transmission is completed. When thetransmitting terminal receives the ACK frame within a predeterminedtime, the transmitting terminal regards that the data transmission issuccessful. However, when the transmitting terminal does not receive theACK frame within the predetermined time, the transmitting terminalregards that the data transmission is failed. Meanwhile, adjacentterminals that receive at least one of the RTS frame and the CTS framein the course of the transmission procedure set a network allocationvector (NAV) and do not perform data transmission until the set NAV isterminated. In this case, the NAV of each terminal may be set based on aduration field of the received RTS frame or CTS frame.

In the course of the aforementioned data transmission procedure, whenthe RTS frame or CTS frame of the terminals is not normally transferredto a target terminal (i.e., a terminal of the receiver address) due to asituation such as interference or a collision, a subsequent process issuspended. The transmitting terminal STA1 that transmitted the RTS frameregards that the data transmission is unavailable and participates in anext contention by being allocated with a new random number. In thiscase, the newly allocated random number may be determined within a range(2*CW) twice larger than a previous predetermined random number range (acontention window, CW).

In the exemplary embodiments given below, a case where a first terminaltransmits an RTS frame to a second terminal may be construed as ameaning that the first terminal transmits the RTS frame in which atransmitter address is an address of the first terminal and a receiveraddress is an address of the second terminal unless otherwise stated.Further, a case where the first terminal transmits a CTS frame to thesecond terminal may be construed as a meaning that the first terminaltransmits the CTS frame in which a receiver address is an address of thesecond terminal unless otherwise stated.

On the other hand, the aforementioned contention-based data transmissionmethods can operate well in an environment with less users, but thecommunication performance is drastically deteriorated in an environmentwhere there are many users to transmit packets. Therefore, a method inwhich a plurality of terminals efficiently transmit and receive data ina dense user environment is required. Hereinafter, methods fortransmitting and receiving data according to embodiments of the presentinvention will be described with reference to each drawing. In theembodiments of the drawings, duplicative description of parts which arethe same as or correspond to the embodiments of the previous drawingswill be omitted.

FIGS. 8 to 10 illustrate a wireless communication method for a terminalusing a distributed access group according to an embodiment of thepresent invention. According to an embodiment of the present invention,the plurality of terminals in a BSS are grouped into at least one groupand data transmissions for terminals may be performed by an allocatedgroup unit.

For the data transmission/reception by a group unit, the AP transmits adistributed access group parameter. The terminals in the BSS havingreceived the distributed access group parameter from the AP startdistributed accesses by the group unit. The distributed access groupparameter triggering a distributed access by the group unit may betransmitted based on an access delay threshold value. When a time takenfor the terminals in the BSS to perform CSMA/CA contention in order totransmit packets is longer than the access delay threshold value, the APmay transmit the distributed access group parameter. For example, when acontention window value allocated to the AP or the terminal in the BSSis longer than the distributed access threshold value, the AP maytransmit the distributed access group parameter. As another embodiment,the AP may obtain information about the number of packet collisions perunit time and when the number of packet collisions is greater than apredetermined reference value, the AP may transmit the distributedaccess group parameter.

The distributed access group parameter may be included in a controlmessage such as a beacon, a probe response, or an association response.According to another embodiment, the AP may transmit the distributedaccess group parameter through a separate trigger frame. The distributedaccess group parameter is a parameter that is referred to by terminalsperforming distributed accesses by a group unit, and includesinformation such as the number of groups assigned to the correspondingBSS, and an inter-group access offset. At this point, information aboutterminals included in each group is designated through the distributedaccess group parameter. The AP may directly designate the terminalsbelonging to each group and transmit the designation information as thedistributed access group parameter. According to another embodiment, theterminal may obtain group information to be allocated to thecorresponding terminal, namely, a group number by using the distributedaccess group parameter received from the AP.

The group number of the terminal may be determined based on identifierinformation (or address information) of the corresponding terminal andinformation of the number of groups. According to an embodiment, thegroup number of the terminal may be determined based on a result valueobtained by modulo-operating the identifier information of thecorresponding terminal with the information of the number of groupsaccording to the following equation.

group number of terminal=mod(identifier information of terminal, thenumber of groups)+1  [Equation 1]

At this point, a MAC address or an association identification (AID)information of the terminal, etc. may be used as the identifierinformation of the terminal. For example, when a MAC address of 48 bitsis used as the identifier information of the terminal, a MAC address of3C-A9-F4-69-43-A4 is represented as a binary number of 0011 1100 10101001 1111 0100 0110 1001 0100 0011 1010 0100. When the number of groupsis 5 and the MAC address is modulo-operated with 5, 4 is obtained as aresult value. At this point, 4, which is the result value of themodulo-operation, is allocated as the group number of the correspondingterminal, or a value (namely, 5) obtained by adding 1 to the resultvalue of the modulo-operation as shown in Equation 1 may be allocated asthe group number of the corresponding terminal.

In this way, when a plurality of terminals are classified into at leastone group, each terminal performs data transmission/reception by eachallocated group unit. According to an embodiment of the presentinvention, during an access period of each group, only designatedterminals in a corresponding group may participate in datatransmission/reception. At this point, each terminal in an identicalgroup may sequentially transmit/receive data or simultaneouslytransmit/receive data using different channels (frequency bands) witheach other. When each terminal sequentially transmits/receives data,each terminal may transmit uplink data by using the above-describedCSMA/CA method during the access period of the corresponding group. Inaddition, when each terminal simultaneously transmits/receives datausing different channels, each terminal may transmit uplink data usingOrthogonal Frequency Domain Multiple Access (OFDMA).

According to an embodiment of the present invention, an access period ofeach group may be continued until the channel is idle for an inter-groupaccess offset time. In other words, when the channel is idle for apredetermined inter-group access offset time, an access period of aprevious group is switched to an access period of a next group.Meanwhile, according to another embodiment, an access period of eachgroup may be set as a fixed time value, or as a time value varying basedon information of the number of designated terminals in the group, etc.

FIG. 8 illustrates an embodiment of a wireless communication method fora terminal using a distributed access group. In the embodiment of FIG.8, the number of STAs for data transmission is set to 6 and the numberof groups is set to 3. In addition, based on the above-described groupnumber determination method, it is assumed that STA1 and STA2 aregrouped into group 1, STA3 and STA4 are grouped into group 2, and STA5and STA6 are grouped into group 3, respectively. Each terminal performsdata transmission and reception according to an access order allocatedfor each group. In the embodiment of FIG. 8, the access order isallocated in the order of group 1, group 2 and group 3, and terminals ofgroup 1 attempt access first.

STA1 and STA2 included in group 1 transmit uplink data using theabove-described CSMA/CA or OFDMA during an access period of group 1.According to an embodiment of the present invention, the uplink datatransmission by non-AP STAs belonging to the corresponding group may belimited to a predetermined number of times (e.g. once), respectively. Atthis point, each non-AP STA may sequentially transmit uplink data duringthe access period or may simultaneously transmit the uplink data usingdifferent channels (frequency bands) with each other. However, the APmay transmit downlink data even in an access period of any group and maytransmit the downlink data without limitation to the number of timeseven in an access period allocated to a specific group.

When data transmission by terminals of a previous group (group 1) iscompleted, no further data transmission is performed and a channelbecomes idle. Each terminal in the BSS performs CCA to check whether achannel is busy and an access period of a next access order group (group2) starts when the channel is maintained in an idle state for aninter-group access offset time. In other words, when the channel is idlefor the inter-group access offset time, terminals of the next group(group 2) may regard that the access period of the previous group (group1) is terminated and attempt to transmit data right after thecorresponding offset time. According to an embodiment of the presentinvention, the inter-group access offset may be set larger than a valueof AIFS for performing a typical backoff procedure. According to anembodiment, the inter-group access offset may be set to a value of twiceor three times the AIFS. According to another embodiment, theinter-group access offset may be set to a value of DIFS+a*CWmax. Here,CWmax is a maximum value of a contention window and ‘a’ is a constant of1 or less. The constant ‘a’ may be changed within a predetermined rangeaccording to channel availability. Each terminal in the BSS may identifythat a group performing data transmission/reception is switched, whenthe inter-group access offset occurs (namely, when a channel is idle forthe inter-group access offset time).

On the other hand, when the inter-group access offset time is set to beshort (e.g. AIFS, etc.), data transmission by a terminal belonging to aprevious group (group 1) may not be completed until the access period ofthe corresponding group (group 1) is terminated. At this point, thecorresponding terminal may participate in contention for uplink datatransmission in an access period of a next group (group 2). In otherwords, a terminal, which starts to perform a backoff procedure in thegroup access period allocated to each terminal, continues to perform thebackoff procedure to attempt data transmission regardless of the accessperiod for each group, until the data transmission is completed.

In the embodiment of FIG. 8, when the access period of group 2 isterminated, an access period of group 3 begins after an inter-groupaccess offset time in the same method. Data transmission/reception by agroup unit may be performed once for each group, or may be repeated aplurality of times. When the data transmission/reception by a group unitis repeated the plurality of times and when an access period of the lastgroup (group 3) is completed, the access period of the first group(group 1) may be resumed. At this point, the repetition numberinformation for data transmission/reception by a group unit may beincluded in a distributed access group parameter.

FIG. 9 illustrates another embodiment of a wireless communication methodfor a terminal using a distributed access group. According to the otherembodiment of the present invention, at least one piece of informationof the distributed access group parameter may be changed during datatransmission/reception by a group unit. According to the embodiment ofFIG. 9, the information of the number of groups of the distributedaccess group parameter may be changed. The AP may set an initial valueof the number of groups according to a predetermined rule and change thenumber of groups according to a status of data transmission/reception bya group unit.

Referring to FIG. 9, the AP transmits a distributed access groupparameter by setting the initial value of the number of groups to 2.Accordingly, terminals in the BSS are classified into two groupsaccording to the aforementioned embodiment and the terminals of group 1first attempt an access according to an access order allocated for eachgroup. However, when a large number of terminals are allocated to onegroup, a time taken for all the terminals of the corresponding group tocomplete data transmission becomes longer and it is highly possible thatcollisions will occur between the terminals during the access period ofthe corresponding group. Accordingly, the AP may increase the number ofgroups used for distributed access by a group unit to reduce the numberof terminals participating in contention in a same time period (namely,the access period).

According to an embodiment, the AP may change the number of groups basedon duration of an access period of an individual group. In other words,the AP may increase the number of groups in the case where a time takenfrom when terminals of the corresponding group start contention for datatransmission to when the inter-group access offset occurs becomes longerthan a predetermined maximum contention time threshold value. When thenumber of groups increases, the updated number of groups may beincreased by 1 from the previous number of groups or twice the previousnumber of groups. However, the present invention is not limited thereto.The AP transmits information of the updated number of groups through thedistributed access group parameter and each terminal which has receivedthe distributed access group parameter newly obtains a group number ofthe corresponding terminal based on information of the updated number ofgroups. According to the embodiment of FIG. 9, the AP increases thenumber of groups from the initial value 2 to 4, and transmits thedistributed access group parameter including the information of theupdated number of groups to each terminal in the BSS through a beacon ora probe response. Each terminal changes a group number thereof andresumes data transmission/reception by a group unit based on theinformation of the update number of groups and the changed group number.

On the contrary, the AP may decrease the number of groups in the casewhere a time (namely, an access time of an individual group) taken fromwhen terminals of the corresponding group start contention for datatransmission to when the inter-group access offset occurs becomesshorter than a predetermined minimum contention time threshold value.When the number of groups decreases, the updated number of groups may bedecreased by 1 from the previous number of groups or by ½ of theprevious number of groups. However, the present invention is not limitedthereto. Accordingly, the AP may prevent the number of occurrences ofthe inter-group access offset from being increased and a channel useefficiency from being lowered due to an excessive number of groups whichexceeds the number of total terminals.

FIG. 10 illustrates another embodiment of a wireless communicationmethod for a terminal using a distributed access group. According to theembodiment of FIG. 10, the distributed access group parameter mayfurther include access start offset information of each group. Theaccess start offset information represents a time after transmission ofthe distributed access group parameter until terminals of thecorresponding group start accesses. Each terminal may obtain a groupnumber of the corresponding terminal and access start offset informationcorresponding thereto, and start uplink data transmission after anaccess start offset time of the corresponding terminal has elapsed fromthe time triggered by the distributed access group parameter.

Referring to FIG. 10, the number of groups is set to 3, terminals ofgroup 1, group 2, and group 3 start data transmission after a time offirst transmission start offset (Offset 1), a second transmission startoffset (Offset 2), and a third transmission start offset (Offset 3)respectively pass. According to an embodiment, a transmission startoffset of each group may be set in uniform intervals or may be set indifferent intervals according to the number of terminals allocated toeach group, etc. When the transmission start offset of each group is setin uniform intervals, in other words, when an access time allocated toeach group is identical, the distributed access group parameter mayinclude group access time information T_gr. Each terminal havingobtained the group access time information T_gr may calculatetransmission start offset information of a group to which thecorresponding terminal belongs by using a group number of thecorresponding terminal and the group access time information T_gr. Forexample, in the embodiment of FIG. 10, a transmission start offset ofgroup 3 may be determined to 2*T_gr+Offset 1. Here, Offset 1 representsa time from a time point triggered by the distributed access groupparameter to the start of an access period of a first group (group 1).

As described above, although data transmission by a terminal of aprevious group is not completed, a transmission start offset time of anext group may arrive and data transmission by terminals of the nextgroup may start. At this point, the terminal of the previous group, inwhich the data transmission has not been completed, may participate incontention for data transmission even in an access period of the nextgroup.

FIG. 11 illustrates a data transmission method using a TIM and PS-Pollin a power saving mode as another embodiment of the present invention.Wireless LAN terminals may be switched into a power save (PS) mode forefficient power management. In the PS mode, each terminal (STA) receivesa traffic indicator map (TIM) that is periodically transmitted by theAP, and checks whether there is data to be received by the correspondingterminal. When the TIM indicates that there is data to be received bythe corresponding terminal, the terminal transmits a PS-Poll to indicatethat data reception is possible. At this point, the terminal transmitsthe PS-Poll by using the above-described CSMA/CA method. In other words,each terminal for transmitting the PS-Poll performs a backoff procedurein a contention window period. A terminal in which a backoff counter hasexpired transmits the PS-Poll and the AP having received the PS-Polltransmits data to the corresponding terminal. After completing datareception, the terminal transmits an acknowledgement (ACK) frame andswitches to a sleep state.

FIG. 12 illustrates a frame structure of a PS-Poll. The PS-polltransmitted by a terminal includes an association ID (AID), a BSSidentifier (BSSID), and a transmitter address (TA) of the correspondingterminal. The AID may be received from the AP in an associationprocedure of a terminal and according to an embodiment, may have amaximum value of 2007. The BSSID indicates a MAC address of the AP withwhich the corresponding terminal is associated and is used as a receiveraddress (RA) of the PS-Poll. The transmitter address indicates a MACaddress of a terminal that transmits the PS-Poll.

According to an embodiment of the present invention, data transmissionfor multi-users may be performed using the TIM and PS-Poll. In moredetail, according to an embodiment of the present invention, efficientdata transmissions/receptions by a plurality of terminals may beperformed through distributed data transmission using multi-channels andat this point, the TIM and PS-Poll may be used. Embodiments hereinaftermay be performed in PS modes of terminals, but the present invention isnot limited thereto and may also be performed in another normal mode ofthe terminals. When the present invention is performed in a normal modeof terminals, in embodiments below, a TIM, a PS-Poll, and a PS pollingperiod may be respectively replaced with a trigger frame, a data requestframe, and a data request frame transmission period.

FIG. 13 illustrates an embodiment of a distributed data transmissionmethod using multi-channels. Referring to FIG. 13, terminals in a PSmode wake up at a time when the TIM is transmitted and receive the TIM.In an embodiment of the present invention, the TIM represents a triggerframe for indicating downlink data to be transmitted to each terminalthrough multi-channels and such a trigger frame may be implemented in atype of frame other than the TIM according to an embodiment. When theTIM indicates that there is data to be transmitted to the correspondingterminal, the terminal transmits a PS-Poll indicating presence of thecorresponding terminal in order to receive the data. Meanwhile, aterminal performs contention through a backoff procedure in order totransmit the PS-Poll. When numerous terminals participate in thecontention, it is highly possible that collisions occur and contentionmay be continued for a long time until successful transmission of thePS-Poll.

Therefore, according to an embodiment of the present invention, PS-Pollsof a plurality of terminals may be transmitted using multi-channels. Inan embodiment of the present invention, the PS-Poll represents a datarequest frame corresponding to the trigger frame and such a data requestframe may be implemented in a type of frame (e.g. PS-Poll′ to bedescribed later) other than the PS-Poll.

According to an embodiment, a target channel through which each terminalwill transmit the PS-Poll may be determined based on an identifier andinformation of the number of available channels of the correspondingterminal. The terminal may obtain channel information operated by the APwith reference to channel width information delivered through a beaconframe. At this point, all or a part of the channels operated by the APmay be designated as available channels. Terminals indicated as havingdata to be received by the TIM may determine the target channels fortransmitting the PS-Poll based on the channel information. In detail,the target channel for transmitting the PS-Poll may be determined basedon a value obtained by module-operating the identifier information ofthe corresponding terminal with the number of available channels. Atthis point, a MAC address, AID information of the terminal, or the likemay be used as the identifier information of the corresponding terminal.When the available channels are consecutively disposed, a channel numberof the target channel through which the PS-Poll is to be transmitted maybe determined as a value obtained by adding a channel number of a firstchannel among the available channels to the obtained value of the modulooperation.

According to another embodiment, a target channel through which eachterminal transmits the PS-Poll may be determined based on an order thatthe corresponding terminal is indicated in the received TIM. A partialvirtual bitmap of the TIM indicates whether there is data to bedelivered to each terminal in the BSS. If there is data to betransmitted to a specific terminal, the corresponding terminal may beindicated with 1. On the other hand, if there is no data to betransmitted, the corresponding terminal may be indicated with 0. At thispoint, the target channel through which each terminal transmits thePS-Poll may be determined in a round robin manner based on an order ofterminals indicated that there is data to be delivered on the partialvirtual bitmap. In other words, on the partial virtual bitmap, CH1(primary channel) may be allocated to a terminal indicated with a first1, and CH2 may be allocated to a terminal indicated with a second 1. Inaddition, when the number of available channels is eight as in theembodiment of FIG. 13, CH2 may be allocated to a terminal indicated witha tenth 1 on the partial virtual bitmap. Such a channel allocationmethod is to determine channel allocation based on a result valueobtained by modulo-operating an indicated order of the correspondingterminal on the partial virtual bitmap with the number of availablechannels. At this point, a channel number of a target channel throughwhich the PS-Poll is to be transmitted may be determined as a valueobtained by adding a channel number of a first channel among theavailable channels to the modulo-operation result value and subtracting1 from the added value.

In this way, when the target channel through which each terminaltransmits the PS-Poll is determined, the terminal performs a backoffprocedure in the determined target channel in order to transmit thePS-Poll. A terminal in which a backoff counter has expired in thebackoff procedure transmits the PS-Poll through the target channel. Whenthe PS-Poll is successfully transmitted, the AP transmits downlink datato the terminal having transmitted the PS-Poll through the correspondingchannel. The terminal transmits a response message after receiving thedownlink data. The above-described operations may be continued until allterminals allocated to each channel transmit the PS-Poll and receivedata. At this point, a series of processes in which the PS-Poll, dataand response message are transmitted may be independently performed foreach channel of the multi-channels. In this way, collision possibilitiesamong terminals may be lowered by distributing channels through whicheach terminal in the BSS transmits the PS-Poll and receives data.Meanwhile, the indication of an interframe space (IFS) between eachtransmission procedure is omitted in FIG. 13, but a predeterminedwaiting time such as AIFS or SIFS, etc. may be set between eachtransmission procedure.

FIG. 14 illustrates a resource allocation method of the AP at the timeof data transmission according to the embodiment of FIG. 13. Accordingto an embodiment of the present invention, the AP may transmit data toeach terminal by using OFDMA. A portion shadowed in FIG. 14 indicates aperiod in which the AP transmits data and the AP uses available channelsto simultaneously transmit data to each terminal by an OFDM symbol unit.Each terminal receives the data through the target channel allocated tothe corresponding terminal among multi-channels.

FIG. 15 illustrates another embodiment of a distributed datatransmission method using multi-channels. When there is a large amountof data to be transmitted, it is efficient to transmit the data by anaggregate MAC protocol data unit (A-MPDU). To this end, according to theembodiment of FIG. 15, a PS polling period and a data transmissionperiod are separately allocated to perform distributed datatransmission. The PS polling period is a period in which the PS-Poll ofeach terminal is transmitted and each terminal is allocated with atarget channel and performs a backoff contention in the allocated targetchannel to transmit the PS-Poll. In addition, the data transmissionperiod is a period in which downlink data is transmitted to terminalssucceeding in PS-Poll transmission.

Duration information of the PS polling period and data transmissionperiod may be transmitted through a beacon, etc. or pre-designated timevalues may be used for them. According to an embodiment of FIG. 15, thePS polling period may be determined to be a time in which one terminalfor each channel may transmit the PS-Poll, for example, AIFS+minimumcontention window value (CWmin)+transmission time of PS-Poll. A terminalwhich succeeds in contention to transmit the PS-Poll may switch to asleep state during a remaining PS polling period to save power. On theother hand, in the PS-Poll transmitted by the terminal, a duration fieldindicating a time until the end of the PS polling period may be set.According to an embodiment, for simultaneous termination of the PSpolling periods, the duration field value of the PS-Poll may bedetermined based on a result obtained by subtracting a backoff countervalue used for transmitting the corresponding PS-Poll from an initiallyset duration value of the PS polling period. Other terminals havingreceived the PS-Poll set a network allocation vector (NAV) based on theduration field value of PS-Poll. In other words, the other terminalshaving received the PS-Poll do not perform data transmission during atime when the PS-Poll is being transmitted and the remaining PS pollingperiod. Accordingly, the terminal having transmitted the PS-Poll mayreceive data from the AP right after the PS polling period is terminatedand the data transmission period is started.

When the PS polling period is terminated, data transmission may bestarted after a SIFS time. During the data transmission period, the APtransmits downlink data to the terminals having transmitted the PS-Pollin the PS polling period. At this point, the AP may simultaneouslytransmit the data to a plurality of terminals through multi-channels.According to an embodiment, the AP may transmit A-MPDU into which datafor a plurality of terminals is aggregated during the data transmissionperiod. On the other hand, between the PS polling period and the datatransmission period, a waiting time other than SIFS, for example, anAIFS may be set.

According to an embodiment of the present invention, the PS pollingperiod and data transmission period may be repeated a plurality oftimes. At this point, information on the number of the repetition isincluded in the TIM to be delivered to each terminal. Terminals havingfailed in PS-Poll transmission in a previous PS polling period mayperform a backoff procedure in order to transmit the PS-poll again in anew PS polling period. At this point, each terminal uses a backoffcounter remaining in the previous polling period or is allocated with anew backoff counter to perform the backoff procedure. According toanother embodiment of the present invention, the number of therepetition may not be separately set and the PS polling period and datatransmission period may be repeated until all terminals indicated in theTIM receive data.

FIG. 16 illustrates another embodiment of a distributed datatransmission method using multi-channels. According to the embodiment ofFIG. 16, a plurality of terminals may transmit a PS-Poll for eachchannel during a PS polling period. At this point, the PS polling periodmay be determined to be sufficiently long such that the plurality ofterminals can transmit the PS-Poll in an identical channel, and eachterminal performs backoff contention in a target channel allocated tothe corresponding terminal to transmit the PS-Poll. In other words, whenthe number of terminals which will transmit the PS-Poll through thetarget channel is plural, a first terminal whose backoff counter expiresfirst transmits the PS-Poll and the remaining terminals wait. When thePS-Poll transmission by the first terminal is completed, the remainingterminals except the first terminal resume the backoff procedure and asecond terminal whose backoff counter expires first in the resumedbackoff procedure may transmit the PS-Poll. Terminals which havesuccessfully transmitted the PS-Poll in the PS polling period may switchto a sleep state during the remaining PS polling period to save power.On the other hand, in the PS-Poll transmitted by the terminal, aduration field indicating a time until the end of the PS polling periodmay be set. Legacy terminals having received the PS-Poll may set a NAVbased on the duration information included in the PS-Poll.

When a predetermined PS polling period is terminated, the AP aggregatesdata to be transmitted to the corresponding terminals based on PS-Pollpackets received during the PS polling period and transmits theaggregated data during the data transmission period. Each terminalhaving transmitted the PS-Poll during the PS polling period receives theaggregated data during the data transmission period and extracts data ofthe corresponding terminal from the aggregated data.

FIG. 17 illustrates an embodiment of a distributed data transmissionmethod using multi-channels. When the terminals that have transmittedthe PS-Poll during the PS polling period are identified, the AP mayaggregate data to be transmitted to the corresponding terminals toconfigure A-MPDU (multi-user A-MPDU). In detail, the AP adds an MPDUdelimiter and a pad before and after an MPDU for each terminal (MPDU1,MPDU2, . . . ) and aggregates them to configure the multi-user A-MPDU.

According to an additional embodiment of the present invention, theaggregated data (the multi-user A-MPDU) transmitted by the AP may beconfigured with a plurality of A-MPDUs (A-MPDU #1 and A-MPDU #2). Atthis point, information of the number of A-MPDUs included in theaggregated data is included in the TIM to be delivered to each terminal.The A-MPDU number including the MPDU for each terminal may be determinedbased on an order of PS-Poll transmission by the corresponding terminal.In other words, the A-MPDU number including the MPDU of a specificterminal may be determined based on a result value obtained bymodulo-operating a PS-Poll transmission order of the correspondingterminal in the PS polling period with the total number of A-MPDUs.

FIG. 18 illustrates another embodiment of a distributed datatransmission method using multi-channels. According to an embodiment ofFIG. 18, the AP may perform contention for data transmission after thePS polling period is terminated. In other words, the AP performs abackoff procedure for data transmission, and when the backoff counterexpires the AP may enter the data transmission period to transmitdownlink data. According to an embodiment, the backoff procedure of theAP is performed only on the primary channel CH1 and on other secondarychannels CH2 to CH8, CCA may be performed to determine whether thecorresponding channels are idle for a PIFS time before the backoffcounter expires. When the backoff counter expires, the AP may usetogether the idle channels that are not occupied by other terminals totransmit the aggregated data (A-MPDU).

FIG. 19 illustrates another embodiment of a data request frame fordistributed data transmission using multi-channels. According to theembodiment of FIG. 19, a modified PS-Poll (PS-Poll′) may be used as thedata request frame.

First, a type and subtype of a frame control field in the PS-Poll′ maybe set as an RTS. Accordingly, legacy terminals having received thePS-Poll′ may set a NAV based on a duration field value thereof. ThePS-Poll′ may include a duration field, a BSS identifier (BSSID), and acombined transmitter address TA′. The duration field indicates a timeuntil the end of the PS polling period. According to an embodiment, forsimultaneous termination of the PS polling period, a duration fieldvalue may be determined based on a result obtained by subtracting abackoff counter value used for transmitting the corresponding PS-Poll′from an initially set duration value of the PS polling period. The BSSIDindicates a MAC address of the AP with which a terminal havingtransmitted the corresponding PS-Poll′ is associated, and is used as areceiver address (RA) of the PS-Poll′.

Next, the combined transmitter address TA′ may include information inwhich an identifier of a terminal having transmitted the correspondingPS-Poll′ and MAC address information of the corresponding terminal arecombined. In detail, the TA′ may include an AID of the correspondingterminal and partial lower information (e.g. lower 3 bytes) of a MACaddress of the corresponding terminal. The upper 3 bytes of the MACaddress of the terminal indicate a vendor ID and the lower 3 bytesthereof indicate an ID of a corresponding network interface card.Accordingly, the PS-Poll′ may include only the lower 3 bytes of a MACaddress used as a TA of an existing PS-Poll in the TA′ field, and mayuse a remaining field of the TA′ for indicating AID information. The APhaving received the PS-Poll′ may identify a terminal that hastransmitted the PS-Poll′ with reference to the AID information andpartial MAC address information of the TA′ field in the correspondingPS-Poll′.

According to an additional embodiment, the TA′ may further include amarker. The marker is an identifier for identifying the PS-Poll′according to an embodiment of the present invention, and an RTS framemay be distinguished from a PS-Poll′ frame based on the marker. Inaddition, the marker indicates whether a transmitter address field ofthe corresponding frame represents a combined transmitter address TA′ ora normal transmitter address TA. Meanwhile, in the embodiment of FIG.19, it is illustrated that the TA′ is configured with a marker of 1byte, an AID of 2 bytes, and partial lower information of MAC address of3 bytes. However this is an embodiment for describing the presentinvention and the present invention is not limited thereto. For example,the TA′ may be configured with AID of 2 bytes and partial lowerinformation of MAC address of 4 bytes.

According to an embodiment of the present invention, data transmissionfor multi-users may be performed using the PS-Poll′. In other words,efficient distributed data transmission for a plurality of terminals maybe performed using a PS-Poll′ additionally including a duration field.FIGS. 20 to 25 illustrate detailed embodiments thereof. In theembodiments below, duplicative descriptions of parts, which are the sameas or corresponding to the embodiments of FIGS. 13 to 18, will beomitted. In other words, the embodiments for PS-Poll transmission inFIGS. 13 to 18 may be replaced with embodiments for PS-Poll′transmission without separate descriptions.

First, FIG. 20 illustrates an embodiment of a distributed datatransmission method using multi-channels. As described above in relationto the embodiment of FIG. 15, the distributed data transmission may beperformed through a separately allocated PS polling period and datatransmission period. When each terminal transmits PS-Poll′ in a PSpolling period, other terminals having received the correspondingPS-Poll′ set NAVs based on a duration field value of the PS-Poll′. Likethe above-described embodiment, the duration field of the PS-Poll′indicates a time until the end of the PS polling period and may bedetermined based on a result obtained by subtracting a backoff countervalue used for transmitting the corresponding PS-Poll′ from an initiallyset duration value of the PS polling period.

When the PS polling period is terminated, data transmission may bestarted after a SIFS time. During the data transmission period, the APtransmits downlink data to terminals having transmitted the PS-Poll′ inthe PS polling period. At this point, the AP may simultaneously transmitdata to a plurality of terminals through multi-channels. On the otherhand, between the PS polling period and the data transmission period, awaiting time other than a SIFS, for example, a waiting time of an AIFSmay be set.

FIG. 21 illustrates an embodiment of a MAC header configuration methodfor indicating distributed data transmission using multi-channels.Referring to FIG. 21, a header of an A-MPDU transmitted by an AP mayinclude available channel information and information indicatingterminals allocated to the corresponding available channel. Theterminals may decode only channels to which the corresponding terminalsare allocated and obtain data therefrom with reference to theinformation included in the header.

The AP may aggregate data to be transmitted to a plurality of terminalsto configure an A-MPDU and transmit the A-MPDU using multi-channels. Atthis point, there may occur a channel in which the AP cannot allocateaccording to a channel occupation status of other users. Since inverseFourier transform/Fourier transform (IFFT/FFT) are performed for theentire band, the AP and terminals are required to obtain informationabout unavailable channels to process data by excluding the decoded bitsin the corresponding channels. Therefore, according to an embodiment ofthe present invention, a MAC header of a first MPDU of the A-MPDU mayinclude the available channel information and information indicatingterminals allocated to the corresponding available channels. Accordingto another embodiment of the present invention, the A-MPDU may beconfigured with data for a plurality of terminals and at this point, theavailable channel information and the information indicating terminalsallocated to the corresponding available channels may be included in aseparate MAC header added at the forefront of the A-MPDU.

Referring to FIG. 21, a MAC header of the present invention may includean OFDMA control field. The OFDMA control field may include theavailable channel information and the information indicating terminalsallocated to the corresponding available channels, and may be set tohave a variable length. According to an embodiment, one bit of a HTcontrol field of the MAC header may be used as an OFDMA control bit. TheOFDMA control bit indicates whether the OFDMA control field according toan embodiment of the present invention is included in the correspondingMAC header and when the corresponding bit is set to 1, the OFDMA controlfield of variable length may follow the HT control field.

The OFDMA control field may include a length field, an allocation bitmapfield and a user indication field. The length field indicates totallength information of the OFDMA control field of variable length and maybe set to have a 1-byte length. The allocation bitmap field indicatesavailable channel information and is set to have 1-byte length torepresent availability for each of total 8 channels in units of 20 MHz.When a channel is not available, a bit corresponding to the channel maybe set to 0, and when the channel is available and data is allocatedthereto, the bit corresponding to the channel may be set to 1. Next, theuser indication field represents information of terminals allocated tothe available channels. In more detail, the user indication field mayinclude information # User of the number of terminals allocated to eachavailable channel and identifier information S-AID of each allocatedterminal. According to an embodiment, partial information of an AID ofthe corresponding terminal, for example, lower 2 bits of the AID may beused as the identifier information S-AID. For example, CH1 and CH3 areindicated as available channels, and MPDUs of STA 1, 2, 3 and 4, andMPDUs of STA 5, 6 and 7 may be respectively allocated to CH1 and CH3 onan allocation bitmap. At this point, first number information # User ofthe user indication field may be set to 4, identifier information S-AIDof STA 1, 2, 3 and 4 may follow thereafter. In addition, next numberinformation # User of the user indication field may be set to 3 andidentifier information S-AID of STA 5, 6 and 7 may follow thereafter.

Meanwhile, as another embodiment of the present invention, the userindication field may indicate an order in which an MPDU of each terminalis positioned in the A-MPDU. At this point, a terminal having obtaineduser indication information may divide the entire A-MDPU into aplurality of MPDUs using MPDU length information included in an MPDUdelimiter and extract an MPDU of the corresponding terminal from amongthe divided MPDUs.

FIG. 22 illustrates another embodiment of a distributed datatransmission method using multi-channels. As described above, the APaggregates data for the terminals having transmitted the PD-Poll′ toconfigure an A-MPDU (multi-user A-MPDU). When MPDUs to be transmitted tothe plurality of terminals are aggregated to configure one A-MPDU, apreamble amount may be reduced, resulting in a reduction in overhead incomparison to the case where the A-MPDU is transmitted by each terminal.The multi-user A-MPDU configured in this way is allocated to a pluralityof OFDM channels and transmitted.

In addition, according to an additional embodiment of the presentinvention, the multi-user A-MPDU may be configured to include aplurality of A-MPDUs A-MPDU #1 and A-MPDU #2. Referring to FIG. 22, apreamble is positioned at a start part of the multi-user A-MPDU and eachof the A-MPDUs A-MPDU #1 and A-MPDU #2 are sequentially disposedthereafter. At this point, a start part of each of the A-MPDUs A-MPDU #1and A-MPDU #2 includes a MAC header HDR according to the foregoingembodiment to indicate available channel information of the multi-userA-MPDU and terminals allocated to the corresponding available channels.Accordingly, a terminal having received the multi-user A-MPDU maydetermine a busy channel with reference to the MAC header HDR of eachA-MPDU. In addition, the terminal may identify a channel in which anMPDU for the corresponding terminal is positioned or an order in whichan MPDU for the corresponding terminal is positioned in the A-MPDU withreference to the MAC header HDR, and may extract and decode the MPDU forthe corresponding terminal based on the identified information.

FIGS. 23 to 25 illustrate embodiments in which distributed datatransmission is performed when some channels are busy in a PS pollingperiod. First, in the embodiments of FIGS. 23 and 24, it is assumed thatthe PS polling period is terminated and data transmission is startedafter a SIFS time. In addition, in the embodiment of FIG. 25, it isassumed that a PS polling period is terminated and an AP performs aseparate backoff procedure in order to perform downlink datatransmission using multi-channels.

First, according to the embodiment of FIG. 23, terminals indicated thatthere is downlink data by TIM may be allocated with channels throughwhich a PS-Poll′ will be transmitted in the same manner as theabove-described embodiment. However, like CH 5 and CH 7, when a channelallocated to a terminal is busy at a start time of a PS polling period,the corresponding terminal may be reallocated with a channel throughwhich the PS-Poll′ is to be transmitted. The terminal may determinewhether each channel is idle at the start time of the PS polling period,and is reallocated with one of the determined idle channels to attemptto transmit the PS-Poll′. According to an embodiment, a new channel maybe allocated based on an order that terminals are allocated to busychannels. In FIG. 23, when a specific terminal allocated to CH 5, whichis in a busy state, is a fourthly allocated terminal in CH 5, thecorresponding terminal may be reallocated to CH 4 that is the fourthamong idle channels. According to the embodiment of FIG. 23, channels CH5 and CH 7, which are in the busy state at a start time of a PS pollingperiod, are excluded from an allocation target and are not to be used inthe PS polling period and data transmission period.

On the other hand, according to an embodiment of FIG. 24, although achannel is busy at a start time of a PS polling period, the channel maybe used in data transmission when becoming idle before a start time of adata transmission period. As described above, when the channel allocatedto the terminal is busy at the start time of the PS polling period, thecorresponding terminal may be reallocated with a channel through which aPS-Poll′ is to be transmitted. However, when channels CH 5 and CH 7 thatare not used for the PS-Poll′ transmission become idle within the PSpolling period, an AP may perform a backoff procedure after an AIFStime. When a channel is idle until a backoff counter of the backoffprocedure expires, the corresponding channel may become a candidatechannel available in the data transmission period. The AP may use achannel CH 5 that is idle even at a start time of the data transmissionperiod among candidate channels as a channel for downlink datatransmission. However, the channel CH 7, which becomes busy due toanother terminal at the start time of the data transmission period amongthe candidate channels, is excluded from a channel for data transmissionby the AP.

Next, according to an embodiment of FIG. 25, the PS polling period isterminated and the AP may perform a backoff procedure in a primarychannel CH1 for data transmission. On the other hand, in other secondarychannels CH2 to CH8, CCA may be performed during a PIFS time before thebackoff counter expires to determine whether corresponding channels areidle. When the backoff counter expires, the AP transmits data using idlechannels that are not occupied by other terminals. Referring to FIG. 25,in a PS polling period, although CH 1 to CH 4, CH 6 and CH 8 that areidle at a PS polling start time are used for PS-Poll′ transmission, CH 1to CH 3 and CH 6 to CH 8 are used for data transmission according to theabove-described backoff procedure in a data transmission period. Inother words, according to embodiments of FIGS. 24 and 25, channels usedin a PS polling period and channels used in a data transmission periodmay be operated independently from each other.

FIG. 26 illustrates a RTS-to-self (hereinafter RTS′) for setting a PSpolling period as another embodiment of the present invention. When a PSpolling period is separately allocated according to the embodiment ofthe present invention, legacy terminals may not identify the duration ofthe corresponding PS polling period. Accordingly, the AP may transmit aseparate RTS′ for setting the PS polling period.

The RTS′ has a frame type of RTS and according to an embodiment, boththe RA and TA may be set to a MAC address of the AP. According toanother embodiment, in the RTS′, the RA may be set to a MAC address ofthe AP and the TA may be set to a predetermined multicast address for aPS-Poll. In addition, a duration field of the RTS′ indicates a timeuntil the end of the PS polling period. Accordingly, legacy terminalshaving received the RTS′ set NAVs based on the duration field thereof.

FIGS. 27 and 28 illustrate methods for performing distributed datatransmission using RTS′. First, in an embodiment of FIG. 27, it isassumed that data transmission is started a SIFS time after a PS pollingperiod is terminated, as shown in the embodiments of FIG. 23 or FIG. 24.In addition, in the embodiment of FIG. 28, it is assumed that the PSpolling period is terminated and an AP performs a separate backoffprocedure in order to perform downlink data transmission usingmulti-channels, as shown in the embodiment of FIG. 25.

In the embodiments of FIGS. 27 and 28, the AP may perform a separatebackoff procedure to transmit a TIM triggering the PS polling period. Atthis point, the backoff procedure is performed on the primary channelCH1 and is started an AIFS time or a PIFS time after a previous sleepstate of the AP is terminated. The AP performs CCA for the secondarychannels CH 2 to CH 8 during a PIFS time before expiration of thebackoff counter, and determines whether the corresponding channels areidle. Next, the AP transmits an RTS′ through a secondary channeldetermined to be idle. In addition, when the backoff counter hasexpired, the AP transmits a TIM through the primary channel CH1 andafter a SIFS, transmits the RTS′.

Legacy terminals having received the RTS′ set NAVs based on a durationfield of the corresponding frame. Accordingly, during the PS pollingperiod, uplink data of the legacy terminals may be prevented from beingtransmitted. However, non-legacy terminals having received the RTS′ donot set NAVs corresponding thereto and may contend for transmitting thePS-Poll (or PS-Poll′) during the PS polling period.

FIG. 29 illustrates another embodiment of a trigger frame for indicatingdownlink data to be transmitted to each terminal through multi-channels.Referring to FIG. 29, a TIM′ in which some information is added to anexisting TIM may be used as the trigger frame.

In detail, the TIM′ includes an Allocation Bitmap field representingavailable channel information and a Polling Opportunity Informationfield representing information about a configuration of the PS pollingperiod. First, the Allocation Bitmap field is set to have a 1-bytelength to represent availability for each of total 8 channels in unitsof 20 MHz. When a channel is not available, a bit corresponding to thechannel is set to 0, and when the channel is available and data isallocated thereto, the bit corresponding to the channel is set to 1.Alternatively, each bit may be set in reverse.

Next, the Polling Opportunity Information field represents informationabout a configuration of a PS-Poll (or PS-Poll′) transmissionopportunity allocated to each terminal in the PS polling period.According to an embodiment of the present invention, the PS-Polltransmission opportunities may be assigned by a predetermined slot unitsuch that PS-Poll transmissions by a plurality of terminals do notoverlap each other during the PS polling period. In other words, the PSpolling period may be configured with at least one slot and a PS-Polltransmission opportunity may be given to one terminal for each slot. Inaddition, the slot may be allocated for each available channel.According to an embodiment, the slot length for PS-Poll transmission maybe determined as a value obtained by adding an xIFS to the time for thePS-Poll transmission. At this point, the xIFS is a margin for ensuringthat the PS-Polls transmitted by terminals do not overlap each other andmay be set such that twice the xIFS is shorter than an AIFS (or a DIFS).Accordingly, in case that a PS-Poll is transmitted at a starting portionof a specific slot and a PS-Poll is transmitted at an end portion of thenext slot such that a corresponding channel is idle for the time oftwice the xIFS, a legacy terminal may be prevented from occupying thecorresponding channel.

The Polling Opportunity Information field may include a slot numberfield, namely, a Number of Opportunity field and a Number of Repetitionfield of the PS-Poll transmission. The slot number field representsinformation on how many slots configure a PS polling period in a timeaxis. In other words, the slot number field represents the number ofslots allocated to each channel in the PS polling period. Accordingly,the duration of the PS polling period may be determined based on a valueobtained by multiplying a slot length by the number of slots. On theother hand, the Number of Repetition field represents information aboutthe number of times that the PS polling period is continuously repeated.When a value of the Number of Repetition field is m, each of the PSpolling period and data transmission period may be sequentially repeatedm times.

FIGS. 30 and 31 illustrate methods for performing distributed datatransmission using the above-described TIM′.

First, referring to FIG. 30, an AP transmits a TIM′ for triggering a PSpolling period. The TIM′ may be included in a beacon to be transmitted,and as shown in the above-described embodiments, the AP may perform aseparate backoff procedure for transmitting the TIM′. The AP performsCCA for each channel during a PIFS before expiration of the backoffcounter to determine whether each channel is idle. The AP sets anallocation bitmap of the TIM′ based on the determined result. In otherwords, channels determined to be idle are indicated as availablechannels in the allocation bitmap and channels determined to be busy areindicated as unavailable channels. The AP transmits the TIM′ set in thisway. At this point, the AP may transmit an RTS′ according to theabove-described embodiment through the channels determined to be idle.Legacy terminals having received the RTS′ set NAVs based on a durationfield of the corresponding frame. Accordingly, during the PS pollingperiod, the transmission of uplink data by the legacy terminals may beprevented. However, non-legacy terminals having received the RTS′ do notset NAVs corresponding thereto and transmit a PS-Poll at a slot timeallocated to the corresponding terminal during the PS polling period.According to an embodiment, a first slot time OP1 of the PS pollingperiod may be started a SIFS time after the reception of the RTS′.

Each terminal having received the TIM′ may obtain slot informationthrough which the corresponding terminal transmits the PS-Poll by usinginformation included in the TIM′. First, the terminal obtains PS pollingperiod sequence information allocated to the corresponding terminal forPS-Poll transmission. When an order in which a specific terminal isindicated on a partial virtual bitmap of the TIM′ is n, the PS pollingperiod sequence j of the corresponding terminal may be determined asbelow.

j=ceil(n/(the number of slots×the number of availablechannels))  [Equation 2]

Herein, ceil (x) denotes a minimum integer that is not smaller than x.In other words, the PS polling period sequence j of the terminal may bedetermined by rounding up a value obtained by dividing an order nindicated for the corresponding terminal on the partial virtual bitmapby a value obtained by multiplying the number of slots for each channelin the PS polling period by the number of available channels. Forexample, as illustrated in FIG. 30, when the number of slots is 7, thenumber of available channels CH1 to CH2, CH4 to CH6, and CH8 is 6, andn=40 for the terminal, the PS polling period sequence j of thecorresponding terminal becomes ceil (40/(7×6))=1 and the correspondingterminal transmits a PS-Poll during a first PS polling period.Similarly, when n=70 for the terminal, the PS polling period sequence jof the corresponding terminal becomes ceil (70/(7×6))=2 and thecorresponding terminal transmits a PS-Poll during a second PS pollingperiod.

The terminal obtains a target channel through which the correspondingterminal transmits the PS-Poll and a target slot number in the allocatedsequence j. To this end, an indication order n′ in the PS polling periodsequence j allocated to the corresponding terminal may be determined asbelow.

n′=n−(j−1)×(the number of slots×the number of availablechannels)  [Equation 3]

In the above-described embodiment, n′=40 in case of n=40, and n′=28 incase of n=70. In other words, the indicated order n′ of thecorresponding terminal in the allocated sequence j may be determined bysubtracting the total number of slots till the previous sequence from anorder n indicated for the corresponding terminal on the partial virtualbitmap.

Next, based on the indicated order n′ in the sequence allocated to theterminal, a target channel k and a slot number s through which thecorresponding terminal transmits a PS-Poll may be determined as below.

k=ceil(n′/the number of slots)  [Equation 4]

s=mod(n′−1,the number of slots)+1  [Equation 5]

Herein, the target channel number k represents a logical channel orderamong the available channels. In other words, the logical channel orderof available channels CH1, CH2, CH4, CH5, CH6 and CH8 in the embodimentof FIG. 30 is respectively allocated as 1, 2, 3, 4, 5, and 6. Forexample, when n=40 for the terminal, n′=40, the target channel k isceil(40/7)=6, and the slot number s is allocated as mod(40−1,7)+1=5.Accordingly, the corresponding terminal transmits the PS-Poll at a 5thslot time OP5 in a 6th logical channel CH8 in a first PS polling period(j=1). Similarly, when n=70 for the terminal, n′=28, the target channelk is ceil (28/7)=4, and the slot number s is allocated as mod(28−1,7)+1=7. Accordingly, the corresponding terminal transmits a PS-Poll at a7th slot time OP7 in a 4th logical channel CH5 in a second PS pollingperiod (j=2). On the other hand, the target channel allocation methodand slot number allocation method according to Equations 4 and 5represent an embodiment of the present invention, but the presentinvention is not limited thereto. For example, according to anotherembodiment of the present invention, a modification may be made suchthat the target channel is allocated based on Equation 5 and the slotnumber is allocated based on Equation 4.

When the PS polling period sequence, the target channel and the slotnumber through which each terminal transmits a PS-Poll are determined,the terminal transmits the PS-Poll in the corresponding sequence,channel and slot time. After one PS polling period, a data transmissionperiod corresponding thereto is started and data is transmitted to aterminal having successfully transmitted the PS-Poll during the PSpolling period. As described above, the PS polling period and datatransmission period are sequentially repeated based on a value of theNumber of Repetition field of a TIM′.

Next, according to an embodiment of FIG. 31, when the number ofterminals which will transmit PS-Poll is smaller than the number oftotal available channels, some of the available channels may not be usedfor transmitting the PS-Poll during the PS polling period. First, thenumber of total PS-Poll transmission opportunities may be obtained basedon repetition number information, available channel (allocation bitmap)information, and slot number information indicated in the TIM′. When thenumber of terminals indicated on the partial virtual bitmap is smallerthan the number of total PS-Poll transmission opportunities, the smallernumber of slots than the number of slots per channel set in the PSpolling period may be required in a channel to which a last indicatedterminal is allocated.

Referring to the second PS polling period of FIG. 31, only 4 slots,which are less than the number of slots 7 allocated per channel, arenecessary for PS-Poll transmission in a channel CH5 to which a lastindicated terminal is allocated on the partial virtual bitmap.Accordingly, a duration field of an RTS′ transmitted through a channelto which the last terminal is allocated may be adjusted based on a slotnumber allocated to the corresponding terminal. In other words, theduration field of the RTS′ transmitted to CH5 during the second PSpolling period is set until a time to a 4th slot OP4. Accordingly, in atime after the 4th slot OP4, other terminals may occupy thecorresponding channel.

Moreover, since no more PS-Poll transmission is performed in channelsCH6 to CH8 following the logical channel CH5 allocated to a terminalindicated last on the partial virtual bitmap, the RTS′ may not betransmitted through the corresponding channels. Accordingly, CH6 to CH8may be occupied by other terminals during the PS polling period. On theother hand, in the channels CH6 to CH8 through which the RTS′ is nottransmitted, CCA may be performed to determine whether the correspondingchannels are idle for a PIFS time before the data transmission period isstarted. When the corresponding channel is idle, the AP may allocatedata thereto and when the corresponding channel is busy, the AP mayexclude the corresponding channel from data allocation.

In this way, according to an embodiment of the present invention, aplurality of terminals may perform non-contention-based datatransmission during a determined period. In other words, each terminalmay not perform contention such as a backoff procedure and may transmita PS-Poll using a target channel and target slot time allocated to eachterminal.

Although the present invention is described by using the wireless LANcommunication as an example, the present invention is not limitedthereto and the present invention may be similarly applied even to othercommunication systems such as cellular communication, and the like.Further, the method, the apparatus, and the system of the presentinvention are described in association with the specific embodiments,but some or all of the components and operations of the presentinvention may be implemented by using a computer system having universalhardware architecture.

The detailed described embodiments of the present invention may beimplemented by various means. For example, the embodiments of thepresent invention may be implemented by a hardware, a firmware, asoftware, or a combination thereof.

In case of the hardware implementation, the method according to theembodiments of the present invention may be implemented by one or moreof Application Specific Integrated Circuits (ASICSs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, micro-controllers, micro-processors,and the like.

In case of the firmware implementation or the software implementation,the method according to the embodiments of the present invention may beimplemented by a module, a procedure, a function, or the like whichperforms the operations described above. Software codes may be stored ina memory and operated by a processor. The processor may be equipped withthe memory internally or externally and the memory may exchange datawith the processor by various publicly known means.

The description of the present invention is used for exemplification andthose skilled in the art will be able to understand that the presentinvention can be easily modified to other detailed forms withoutchanging the technical idea or an essential feature thereof. Thus, it isto be appreciated that the embodiments described above are intended tobe illustrative in every sense, and not restrictive. For example, eachcomponent described as a single type may be implemented to bedistributed and similarly, components described to be distributed mayalso be implemented in an associated form.

The scope of the present invention is represented by the claims to bedescribed below rather than the detailed description, and it is to beinterpreted that the meaning and scope of the claims and all the changesor modified forms derived from the equivalents thereof come within thescope of the present invention.

[Mode for Invention]

As above, related features have been described in the best mode.

INDUSTRIAL APPLICABILITY

Various exemplary embodiments of the present invention have beendescribed with reference to an IEEE 802.11 system, but the presentinvention is not limited thereto and the present invention can beapplied to various types of mobile communication apparatus, mobilecommunication system, and the like.

1. A wireless communication method for a terminal comprising: receivinga distributed access group parameter for data transmission/reception bya group unit, wherein the distributed access group parameter comprisesinformation of the number of groups assigned to a corresponding BSS;obtaining group information of the terminal based on the distributedaccess group parameter; and performing data transmission based on theobtained group information.
 2. The wireless communication method ofclaim 1, wherein the performing data transmission is characterized inthat at least one terminal having identical group informationparticipates in the performing of the data transmission during apredetermined access period.
 3. The wireless communication method ofclaim 2, wherein the at least one terminal having the identical groupinformation simultaneously transmits data by using different channelswith each other.
 4. The wireless communication method of claim 2,wherein the at least one terminal having the identical group informationsequentially transmits data.
 5. The wireless communication method ofclaim 1, wherein the at least one terminal having identical groupinformation performs a backoff procedure for the data transmissionduring the predetermined access period.
 6. The wireless communicationmethod of claim 5, wherein the distributed access group parameterfurther comprises inter-group access offset information, wherein thepredetermined access period is terminated when a channel is idle for theinter-group access offset time.
 7. The wireless communication method ofclaim 5, wherein the predetermined access period is set to be a fixedtime value.
 8. The wireless communication method of claim 5, whereinwhen the predetermined access period is terminated, terminals havinggroup information of a next access order participate in the datatransmission.
 9. The wireless communication method of claim 1, whereinthe group information of the terminal is determined based on informationof the number of groups and identifier information of the terminal. 10.The wireless communication method of claim 9, wherein the groupinformation of the terminal is determined based on a value obtained bymodulo-operating the identifier information of the terminal with thenumber of groups.
 11. The wireless communication method of claim 1,wherein the information of the number of groups is changed based on aduration of an access period of an individual group.
 12. The wirelesscommunication method of claim 1, wherein the distributed access groupparameter is transmitted through a beacon or a probe response.
 13. Thewireless communication method of claim 1, wherein the distributed accessgroup parameter further comprises access start offset informationrepresenting a time point at which terminals of each group start access.14. A wireless communication terminal comprising: a transceiverconfigured to transmit and receive a wireless signal; and a processorconfigured to control an operation of the terminal, wherein theprocessor is further configured to: receive a distributed access groupparameter for data transmission/reception by a group unit, thedistributed access group parameter comprising information of the numberof groups assigned to a corresponding BSS, obtain group information ofthe terminal based on the distributed access group parameter, andperform data transmission based on the obtained group information.